This application claims the priority of PCT Application No. PCT/CH96/00248, filed Jul. 5, 1996, which is incorporated herein by reference.
The present invention relates to an injection device for injecting fluid according to the preamble of claim 1.
Syringe-shaped injection devices for injecting fluids have been known for some time. They contain a bushing-shaped main body which can be screwed together at approximately the centre and can be divided into two main sections:
a distal section (facing away from the patient) containing the discharge mechanism and comprising at least one rod-shaped driven member having a structured surface (e.g. a screw rod), a hollow cylindrical counter component corresponding to the driven member, provided with a structured internal sleeve (e.g. a screw nut) and a control button; and
a proximal section (facing the patient) containing the fluid to be administered and a displaceable piston.
At the proximal end of the main body, a needle and a needle holder are attached, allowing the fluid to be discharged from the device; known needles of this type are for instance PENFINE(copyright) needles as described in WO95/01812. The connecting member between the proximal and the distal section of the main body is the driven member, shifting the piston by the selected dose in proximal direction, which causes a discharging of the fluid through the needle.
Often the fluid to be injected is not directly contained in the main body but in an ampoule, with the fluid being stored between a pierceable membrane and a piston displaceable by sliding.
Depending on the injection device, various features are expected from the discharge mechanism. There are devices allowing only a single discharge, devices allowing several discharges of the same dose and devices allowing freely selectable discharges.
For patients using injection devices allowing a change of ampoules, it isxe2x80x94irrespective of the complexity of the discharge mechanismxe2x80x94extremely difficult to wind back the driven member to the initial position in order to make the device ready for operation after the ampoule has been changed. Devices requiring the driven member to be rewound by the control button are known from WO93/16740.
Devices allowing the threaded rod to be pushed back, as in publications U.S. Pat. No. 4,592,745 and EP-A-0 554 995, are more easily operated by patients. The disadvantage of these prior art devices is that due to the release of the distal section from the proximal section of the main body the threaded nut is spread, allowing the threaded rod to move freely without any conscious operation by the patient, with screwing together of both sections of the main body after replacement of the ampoule easily causing a premature unintentional discharge of fluid. Depending on the injection device, this could also result in an incorrect dosing which, in case of certain medication, could prove extremely hazardous to the patient""s health.
The invention aims to remedy this situation. It is the object of the invention to provide an injection device in which the sliding back of the driven member requires a conscious operation by the patient, which releases the driven member and counter component from each other to prevent the hazard of an incorrect dosing.
The invention solves the set task with an injection device comprising the characteristics of claim 1.
The advantages achieved by the invention lie mainly in the fact that the free return or free back sliding of the driven memberxe2x80x94without the need for additional control elements to be mountedxe2x80x94is only possible when the patient releases the driven member by turning it, i.e. by a conscious additional operation.